1. Field of the Invention
The present invention relates to vehicle wheels and more particularly to a method for manufacturing lightweight automotive wheels. Still more particularly, the present invention is directed to a method for manufacturing one-piece vehicle wheels.
2. Description of the Prior Art
A perspective view of a typical automotive wheel 10 is shown in FIG. 1, and FIG. 2 shows a cross-sectional view along a diametral plane A--A of the wheel. The wheel 10 includes a rim 12 and a hub 14. The rim 12 and the hub 14 typically have a contoured cross-sectional shape, as shown in FIG. 2, for structural as well as asthetic purposes. The rim 12 includes two rim portions 16 and 18 which are usually of different length. Flanges 20 are provided at the edges of the rim portions 16 and 18 for retaining an inflatable tire (not shown) to the periphery of the rim 12.
Automotive wheels are most commonly formed of two or three pieces, including a hub section and one or two rim sections. However, a number of attempts have been made to produce one-piece automotive wheels from lightweight materials such as aluminum. U.K. Patent No. 2063722A to Victor discloses a method of manufacturing vehicle wheels starting from a blank in the form of a circular sheet of lightweight metal. Referring to FIGS. 3a and 3b, the hub 24 of the wheel is formed by shaping the center portion 26 of a blank 22. The rim of the wheel is formed by splitting the peripheral portion 28 of the blank 22 in a radial direction along a plane passing through the blank to form two annular split portions 30 and 32 of equal length and different thickness (FIG. 3c), and these portions are subsequently formed by a rolling-pressing operation into rim portions 34 and 36, respectively, of equal thickness and of different lengths (FIG. 3d). Specifically, the rim portion 36 which corresponds to the thicker split portion 32 is longer than the rim portion 34 which corresponds to the split 30.
U.S. Pat. No. 4,532,786 to Schaible discloses another method of manufacturing vehicle wheels from a circular metal blank. Referring to FIG. 4, in Schaible, the peripheral portion 38 of a blank 40 is bent at the edge at 42 (FIGS. 4a and 4b). The peripheral portion 38 is the into two annular split portions 44 and 46 of different thickness, with one of the portion 46 having the bend 42 at its end (FIG. 4c). The split portions 44 and 46 are then lengthened by a rolling-pressing operation into rim portions 48 and 50, respectively, of equal thickness but of different lengths (FIG. 4d). In this case, the rim portion 50 which corresponds to the split portion 46 is longer than the rim portion 48 which corresponds to the split portion 44 because the split portion 46 has more material, as compared to the split portion 44, due to the bend 42 at its end.
One problem encountered in forming a split rim wheel is that it is difficult to obtain a precise split so that the proper amount of material is available to form each rim portion. Typically, the splitting operation is performed with a cutting roller. It is difficult to accurately control the roller with respect to the blank, especially since the blank may flex during the splitting operation.
It is noted that during the splitting operation, in order to allow the split portions to spread out away from the plane of the peripheral portion, no support can be provided against the surfaces of the peripheral portion to rigidly maintain the peripheral portion when it is split. In addition, it has been found that the interaction between the tool bit and an angled surface (such as in Schaible) can misguide the tool bit and give rise to inconsistent thickness of the split portions.